The system reflects the movement of the mouse by moving the cursor on the screen accordingly. As the cursor moves over different parts of windows or into different windows, the system (or an application) changes the appearance of the cursor. For example, when the cursor crosses a window border, the system changes the cursor into a two-headed arrow.
If the system does not have a mouse, the system displays and moves the cursor only when the user chooses certain system commands, such as those used to size or move a window. To provide the user with a method of displaying and moving the cursor when a mouse isn't available, an application can use the cursor functions to simulate mouse movement. Given this simulation capability, the user can use the arrow keys to move the cursor.